High temperature high strength alloys



United States Patent 2,704,250 HIGH TEMPERATURE HIGH STRENGTH ALLOYS Peter Payson, New York, N. Y., assignor to Crucible Steel Company of America, New York, N. Y., a corporation of New Jersey No Drawing. Application December 3, 1948, Serial No. 63,449

14 Claims. (Cl. 75-171) This invention pertains to aHoys having high strength at high temperatures, and more particularly to cobalt base alloys, characterized by high resistance to rupture under stress at temperatures upward of 1600 F.

The invention provides a new and improved corrosion and oxidation resistant, forgeable alloy of this type which is far superior to those previously known as regards resistance to rupture under stress at elevated temperatures of the order aforesaid.

The new forgeable alloy of the invention comprises about 45 to 58% cobalt, about 7 to 12% nickel, about 17 to 22% chromium, about 8 to 18% in aggregate of 2,704,250 Patented Mar. 15, 1955 It has been established that cobalt is very effective in raising the strength of alloys at high temperatures, and the best of the high temperature alloys contain upwards of cobalt. The best of the forgeable alloys now available also contain upward of 1% columbium (or tantalum). Both cobalt and columbium are in short supply and the quantities available would be insufficient for a large demand such as might develop in war time. Consequently it is desirable to provide alloys of the desired properties without the use of cobalt and columbium, or with the use of relatively small amounts of these elements. Unfortunately, it at present seems impossible to develop an alloy for service at very high temperatures without the use of an appreciable amount of cobalt. On the other hand, the present invention shows that a forgeable cobalt-chromium-nickel alloy with suitable amounts of tungsten and molybdenum, and containing less than 1% of columbium has much better strength at 1700 F., than forgeable alloys now available.

The relative value of an alloy for service at 1700 F. under high stress can be established quickly and conveniently by testing the alloy for time-to-rupture at 1700 F. under a stress of 12,000 P. S. I. For example, the alloys designated as N 155 and S 816 in the article referred to above, and having the analyses shown below, have the rupture times shown in Table I.

Table I.Rupture times of prior art forgeable alloys Analysis, Percent Hrs. to

Rupture Grade at 1,700 F. 0 Ni Or w Mo Ob Ti N 00 Ba]. f N155 .12 20.3 20.4 2.0 3.4 1.1 .14 19.7 Fe 16.4 S816 .39 21.1 20.6 4.4 3.7 3.9 42.3 Fe 42.7

metal of the group tungsten and molybdenum, with an It is clear from these values that the higher cobalt alloy upper limit of about 16% for each element. The alloy has a much longer life under these conditions of temmay also advantageously contain from effective amounts 40 perature and stress. A further indication of the effecup to about 1% each of either columbium and titanium, tiveness of substantial amounts of cobalt in raising the or up to about 1.5% in aggregate of both of these elehigh temperature strength of alloys is given in Table H, ments. In addition manganese may advantageously be based on tests made in connection with the present addgd up tobabout 2%; and gillconsltl; to about 1%}; invention. Car on may e present up to a out 0. a consistent wit 6 o retention of forgeability, the balance of the composition Table H' Eflect of Cobalt to at 1700 being substantially iron except for the'usual impurities within commercial tolerance. The invention also em- Analysis, Percent Hrs. to braces cast articles of the above analysis with the modi- Alloy fi fi wfi fications that carbon may be present up to about 0.7%, 0 Ni or W Mo 00 Ba] and12,000 while the aggregate content of tungsten and molybdenum P- may be increased in the upper limit up to about 25%.

In recent years because of the development of gas WF13 .18 27.2 19.0 6.9 5.6 10.8 Fe 2.5 turbines and jet propelled aircraft, there has been a WF 16 1&2 Fe 65 growing need for metals of high strength at high temperatures. Considerable research has been carried out in many laboratories and some alloys have been developed which have good strength at 1700 F. and higher; for example, the alloy designated X 40 in the article, Heat Resistant Alloys from 1200 to 1800F, by N. J. Grant, A. F. Frederickson, and N. E. Taylor published in the March 18, April 8, and April 15, 1948, issues of Iron Age. However, this alloy containing 0.5 carbon, 10 nickel, 25 chromium, 7 tungsten, cobalt, and balance iron is available only as castings, and alloys which can be produced in forged and rolled sections are desired. For example, sheets are required of high strength and oxidation resistance at high temperature for combustion chamber liners in gas turbines, and for tail cone assemblies in jet propelled aircraft. As stated in the article referred to above, the best of the forgeable alloys, S-816, containing 0.14 C, 20 Ni, 20 Cr, 4 W, 4 Mo, 4 Ch, 45 Co, balance Fe, has a 100 hour stress rupture value of less than 10,000 pounds per square inch (P. S. I.) at 1700 F.

It is the object of this invention to provide a forgeable alloy which has a 100 hour stress rupture value of about 12,000 P. S. I. at 1700 F. It is another object of this invention to provide an alloy of these properties which contains as little as possible of the strategic element columbium.

Chromium is required in high temperature alloys to provide resistance to oxidation of the alloys at elevated temperatures. But chromium is also eflective in increasing the rupture time of such alloys as shown in the Table III test results below.

Table [IL-Effect of chromium in cobalt-tungsten alloy on time to rupture at 1700 F.

Analysis, Percent Hrs. to

- Rupture Alloy at 1,700 F. 0 01' v w 00 Bal. and 12,900

WF 1 29 4. 7 .4 19. 2 41.2 Fe 1.8 34 9. 7 5 19. 1 40. 5 Fe 8. 7 34 15.0 .4 19. 0 42.8 Fe 12.7 36 20. 7 5 18. 8 41. 7 Fe 25. 7

These results show that rupture time increases appreciably with increasing chromium but it has been established that cobalt alloys containing chromium over about 22% are very difiicult to forge and therefore the chromium in the alloy of this invention is preferably limited-to about 22% on the high side, and to about 17% on the low side.

The elements besides cobalt and chromium required to provide high strength at high temperatures are the carbide forming elements, particularly tungsten and 4 Table VI.-Eflects of manganese and nickel in alloy of high strength properties on time to rupture at 1700 F.

molybdenum as shown by the test results of Table IV. 6 Analysis Percent Hrs. to

Rupture Table lV.-Efiects of tungsten and molybdenum on Y 2 3593? time to rupture at 1700 F. M11 N1 01 W 0 00 B81 :12 a 2;: a; as a a: a at was as a s as .22 2'3 C w s.'1. WF 45.. I20 513 1111 2014 1013 614 42:0 Fe 30.5

17.6 Fe 1.7 15 18,4 Fe 4,9 Although Alloy WF 37 has a somewhat better rupture F6 time than Alloy WF 18, the composition of the latter {2'2 2:2 is preferred because the saving of about cobalt in 1838 Fe 40.3 the latter by a substitution of 10% nickel, is considered 187 F8 1&2 adequate compensation for the relatively small difference in rupture time.

Another worthwhile and surprisng improvement in the These data show that although the life of the alloy inalloy of thisinvention is brought about by the use of creases appreciably with increase in tungsten and molybsmall quantmes, a Is 111 amounts 1 t about e h. denum f Zero to about f each, a f rth r of the strong carbrde formers columblurn and tltamum,

as shown in Table VII.

Table VIL-Bfieets of columbium and titanium in alloy of high strength properties on time to rupture at 1700 F.

Analysts, Percent Hrs. to

Rupture at Alloy 1,700 F.

0 Mn Ni Cr w Mo 0b T1 00 Bal. g

WF 17 .18 1.6 10. 2 19. 6 10.0 3.0 52. 0 Fe 26. 9 WF 19 1. 6 10. 2 l9. 0 10. 4 2. 7 51. 5 Fe 40. 4 WF 29"--. 16 1. 5 10. 5 20.5 9. 6 2. 5 18 49. 0 Fe 46. 9 WF 30 .18 1. 5 l0. 0 20. 1 9. 6 2. (i 77 50.3 Fe 44. 3 WF 31..... .19 1.4 10.3 20.0 10.3 2.7 .76 48.5 Fe 90.9 WF 32..-" 16 1.0 10. 4 20.3 10. 2 2.7 .35 18 48.6 Fe 125.8

crease from about 10% to 16% of each element has little advantage, and indeed is a disadvantage from the viewpoint of forgeability.

Combinations of tungsten and molybdenum are also effective in producing resistance to rupture at 1700 F. in these alloys as shown in Table V.

Table V.--Eflects of combinations of tungsten and molybdenum on time to rupture at 1700 F.

Analysis, Percent Hrs. to

Rupture Alloy at 1,700 F.

0 Ni Cr w Mo 00 Bal E were not successful. In the first place alloys containing so desired amounts of Co, W, and Mo, and over about 6% Mn, or over about 12% Ni, were very difficult to forge. Furthermore as shown in Table VI below, the maximum useful amounts of manganese and nickel were found to be about 2 and 12% respectively.

These alloys may be used in the annealed condition or the precipitation-hardened condition. The former is produced by heating the alloy to about 2250 F. and cooling it very slowly down to about 1800 F. and then cooling in air thereafter. The latter is produced by heating the alloy to about 2250 F., then cooling it to room temperature rapidly in water, oil, or air; then reheating it at 1600 to 1900 F., depending on the service temperature. The precipitation hardening treatment is generally preferred.

The alloys of this invention have been produced in bar and sheet form by commercial methods. The cogging temperature is about 2200 F. The rolling temperature for sheet slabs is about 2150" F., and the finishing temperature about 1500 F.

What I claim as new is:

1. A cobalt base alloy characterized by high resistance to rupture under stress at temperatures upward of 1600 F., said alloy having substantially the following composition: 45 to 58% cobalt; 7 to under 12% nickel; 17 to 22% chromium; 8 to 25% in aggregate of at least one metal selected from the group consisting of tungsten and molybdenum, with an upper limit of 16% for each said element; carbon under 0.3%; and the balance iron.

2. A cobalt base alloy characterized by high resistance to rupture under stress at temperatures upward of 1600 F., said alloy having substantially the following composition: 45 to 58% cobalt; 7 to under 12% nickel; 17 to 22% chromium; 8 to 25% in aggregate of at least one metal selected from the group consisting of tungsten and molybdenum, with an upper limit of about 16% for each of said element; up to 1.5% in aggregate of at least one metal selected from the group consisting of columbium and titanium for increasing the elevated temperature strength of the alloy, with an upper limit of 1% for each said element; manganese up to 2%; silicon up to 1%; carbon up to 0.3%; and the balance iron.

3. A cast article made of a cobalt base alloy characterized by high resistance to rupture under stress at temperatures upward of 1600 F., said alloy having substantially the following composition: 45 to 58% cobalt;

7 to under 12% nickel; 17 to 22% chromium; 8 to 25% in aggregate of at least one metal selected from the group consisting of tungsten and molybdenum, with an upper limit of 16% for each said element; carbon up to 0.3%; and the balance iron.

4. A cast article made of a cobalt base alloy characterized by high resistance to rupture under stress at temperatures upward of 1600" F., said alloy having substantially the following composition: 45 to 58% cobalt; 7 to under 12% nickel; 17 to 22% chromium; 8 to 25 in aggregate of at least one metal selected from the group consisting of tungsten and molybdenum, with an upper limit of 16% for each said element; from an effective amount up to 1.5% in aggregate of at least one metal selected from the group consisting of columbium and titanium for increasing the elevated temperature strength of the alloy, with an upper limit of 1% for each said element; manganese up to 2%; silicon up to 1%; carbon up to 0.3%; and the balance iron.

5. A forgeable, cobalt base alloy characterized by high resistance to rupture under stress at temperatures upward of 1600 B, said alloy having substantially the following composition: 45 to 58% cobalt; 7 to under 12% nickel; 17 to 22% chromium; 8 to 18% in aggregate of at least one metal selected from the group consisting of tungsten and molybdenum, with an upper limit of 16% for each said element; carbon up to 0.3%; and the balance iron.

6. A forgeable, cobalt base alloy characterized by high resistance to rupture under stress at temperatures upward of 1600 F., said alloy having substantially the following composition: 45 to 58% cobalt; 7 to under 12% nickel; 17 to 22% chromium; 8 to 18% in aggregate of at least one metal selected from the group consisting of tungsten and molybdenum, with an upper limit of 16% for each said element; up to 1.5% in aggregate of at least one metal selected from the group consisting of columbium and titanium for increasing the elevated temperature strength of the alloy, with an upper limit of about 1% for each said element; manganese up to 2%; silicon up to 1%; carbon up to 0.3%; and the balance iron.

7. A cobalt base alloy characterized by high resistance to rupture under stress at temperatures upward of 1600 F., said alloy having substantially the following composition: 45 to 58% cobalt; 7 to under 12% nickel; 17 to 22% chromium; 8 to 25% in aggregate of at least one metal selected from the group consisting of tungsten and molybdenum, with an upper limit of 16% for each said element; from an effective amount up to 1.5 in aggregate of at least one metal selected from the group consisting of columbium and titanium for increasing the elevated temperature strength of the alloy, with an upper limit of 1% for each said element; manganese up to 2%; silicon up to 1%; carbon up to 0.3%; and the balance HIGH.

8. -A forgeable, cobalt base alloy characterized by high resistance to rupture under stress at temperatures upward of 1600 F., said alloy having substantially the following composition: 45 to 58% cobalt; 7 to under 12% nickel; 17 to 22% chromium; 8 to 18% in aggregate of at least one metal selected from the group consisting of tungsten and molybdenum, with an upper limit of 16% for each said element; from an effective amount up to 1.5% in aggregate of at least one metal selected from the group consisting of columbium and titanium for increasing the elevated temperature strength of the alloy, with an upper limit of 1% for each said element; manganese up to 2%; silicon up to 1%; carbon up to 0.3%; and the balance iron.

9. A cobalt base alloy consisting of 18 to 22% chromium, l216% tungsten, 0.02 to .25% carbon, silicon up to 1%, 0.25 to less than 2% manganese, 8 to 12% nickel, to 55% cobalt, and up to 5% iron.

10. An alloy consisting of 17 to 20% chromium, 4 to 16% tungsten, 6.5 to 16% molybdenum, with the total molybdenum and tungsten not greater than 25%, carbon 0.02 to 0.2%, silicon 0.4 to 1%, manganese 0.4 to 2%, nickel 9 to 12%, cobalt 45 to and iron 0.1 to 1%.

11. A cobalt base alloy consisting of 1822% chromium, 1216% tungsten, 0.02-25% carbon, silicon up to 1%, 0.25 to less than 2% manganese, 812% nickel, 4555% cobalt, up to 5% iron, up to 3% molybdenum, and up to 1.5% of metal of the group columbium, tantalum and titanium.

12. An alloy consisting of 17 to 20% chromium, 4 to 16% tungsten, 6.5 to 16% molybdenum with the total molybdenum and tungsten not greater than 25 carbon 0.02 to 0.2%, silicon 0.4 to 1%, manganese 0.4 to 2%, nickel 9 to 12%, cobalt 45 to 50%, and iron 0.1 to 1%, the tungsten and molybdenum being present in the relation that the tungsten to molybdenum ratio is in the range of 0.5 to 1.2%.

13. An alloy consisting of 17 to 20% chromium, 4 to 16% tungsten, 6.5 to 16% molybdenum with the total molybdenum and tungsten not greater than 25%, carbon 0:02 to 0.2%, silicon 0.4 to 1%, manganese 0.4 to 2%, nickel 9 to 12%, cobalt 45 to 50%, and iron 0.1 to 1%, the tungsten and molybdenum being present in the relation that the tungsten to molybdenum ratio is in the range of 0.8 to 1.2%.

14. An alloy consisting of 17 to 20% chromium, 4 to 16% tungsten, 6.5 to 16% molybdenum with the total molybdenum and tungsten not greater than 25%, carbon 0.02 to 0.2%, silicon 0.4 to 1%, manganese 0.4 to 2%, nickel 9 to 12%, cobalt 45 to 50% and iron 0.1 to 1%, the tungsten and molybdenum being present in the relation that the tungsten to molybdenum ratio is in the range of 0.8 to 1.2, the iron plus manganese plus silicon content being equal to 1.5% to 3%.

References Cited in the file of this patent UNITED STATES PATENTS 2,246,078 Rohn el'. al June 17, 1941 2,432,615 lFranks et al Dec. 16, 1947 2,684,299 Binder July 20, 1954 OTHER REFERENCES Symposium on Materials for Gas Turbines, 1946, page 29; published by American Society for Testing Materials. 

1. A COBALT BASE ALLOY CHARACTERIZED BY HIGH RESISTANCE TO RUPTURE UNDER STRESS AT TEMPERATURES UPWARD OF 1600* F., SAID ALLOY HAVING SUBSTANTIALLY THE FOLLOWING COMPOSITION: 45 TO 58% COBALT; 7 TO UNDER 12% NICKEL; 17 TO 22% CHROMIUM; 8 TO 25% IN AGGREGATE OF AT LEAST ONE JMETAL SELECTED FROM THE GROUP CONSISTING OF TUNGSTEN AND MOLYBDENUM, WITH AND UPPER LIMIT OF 16% FOR EACH SAID ELEMENT; CARBON UNDER 0.3%; AND THE BALANCE IRON. 